Plant Doctor Archive

Blackcurrant bushes in a bad way

We have recently moved house and our new place has three blackcurrant bushes. They look in a bad way — looks like lots of rust on the leaves and not good leaf colour. What do we do and when should we do it?

Blackcurrants (Ribes nigra) are usually quite easy to grow, but do prefer cooler and drier conditions. If you are living in a warmer, wetter area, or if it has been wetter than usual (which it has), it is likely that the blackcurrant bushes are suffering from fungal attack. There are four likely culprits — downy mildew (grey fluff), powdery mildew (powdery deposits on the leaves), rust (rusty-orange deposits on the leaves) or leafspot (yellowed spots on the leaves). All four diseases would cause discolouration of the leaves. Other possibilities are aphids or mites, or, worst of all, a virus.

What to do: If you have a fungus and can work out which one it is, then choose an appropriate fungicide and follow the instructions. Prune back and destroy old shoots to promote healthy new growth. Make sure the bushes have at least some sun, have good air movement through their stems and fertilise well in the growing season with potash and nitrogen.

If you can see insects or mites, then you will need an insecticide or miticide. Check carefully for the instructions with regard to flowering (i.e. bees) and eating the fruit after spraying.

If you have a virus you may need to remove and destroy the old plants. There are new resistant varieties available.

Advice by Dr Dan Blanchon from Unitec's Diploma in Sustainable Horticulture and Bachelor of Resource Management.

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